Pilot Scheme for a MIMO Communication System

ABSTRACT

The present invention employs a pilot scheme for frequency division multiple access (FDM) communication systems, such as single carrier FDM communication systems. A given transmit time interval will include numerous traffic symbols and two or more short pilot symbols, which are spaced apart from one another by at least one traffic symbol and will have a Fourier transform length that is less than the Fourier transform length of any given traffic symbol. Multiple transmitters will generate pilot information and modulate the pilot information onto sub-carriers of the short pilot symbols in an orthogonal manner. Each transmitter may use different sub-carriers within the time and frequency domain, which is encompassed by the short pilot symbols within the transmit time interval. Alternatively, each transmitter may uniquely encode the pilot information using a unique code division multiplexed code and modulate the encoded pilot information onto common sub-carriers of the short pilot symbols.

This application is a continuation of U.S. patent application Ser. No.13/721,784, filed Dec. 20, 2012, which is a continuation of and claimspriority to U.S. patent application Ser. No. 12/088,589, filed Jun. 5,2008, which is a National Phase Application under 35 USC 371 ofPCT/IB2006/002714, filed Sep. 29, 2006, which claims the benefit of U.S.provisional patent application Ser. No. 60/722,807, filed Sep. 30, 2005;and U.S. provisional patent application Ser. No. 60/824,158, filed Aug.31, 2006, all of which are incorporated herein by reference as if setforth in their entireties.

FIELD OF THE INVENTION

The present invention relates to communications, and more particularlyrelates to providing a regular or virtual multiple input multiple output(MIMO) communication environment and user elements using a novel pilotsignal scheme.

BACKGROUND OF THE INVENTION

With the ever-increasing demand for wireless transmission capacity basedon the number of users able to access a system or the speed at whichdata is transferred, multiple input multiple output (MIMO) architectureshave evolved. MIMO architectures incorporate multiple antennas fortransmission and multiple receivers for reception. In combination withvarious coding techniques, the spatial diversity provided by MIMOsystems provides for significant increases in the number of users thatcan access a system at any given time, as well as the amount of datathat can be transmitted over a given period of time. Unfortunately, thenature of mobile communications dictates the need for inexpensive userelements, such as mobile telephones, wireless personal digitalassistants (PDAs), and the like. Implementing multiple antennas andtransmission paths within user elements significantly increases theircomplexity, and thus price. For certain applications, the priceassociated with providing multiple antennas and transmission paths inuser elements has significantly outweighed the benefit of more capacity.In other applications, the benefits of MIMO-based communications warrantproviding multiple antennas and transmission paths.

Most base stations are already equipped with multiple antennas andreceivers, and given the nature of such infrastructure, the cost ofproviding such has proven largely insignificant. Thus, there exists awireless infrastructure capable of facilitating MIMO-basedcommunication, yet certain consumers are unwilling to bear the cost ofcompleting the MIMO environment by buying properly equipped userelements. As such, there is a need to reap the benefit of MIMO-basedcommunications without requiring all user elements to have multipleantennas and transmission paths. There is a further need to provide moreefficient and effective ways to facilitate MIMO-based communicationsbetween base stations and different types of user elements.

SUMMARY OF THE INVENTION

The present invention employs a pilot scheme for frequency divisionmultiple access (FDM) communication systems, such as single carrier FDMcommunication systems. A given transmit time interval will includenumerous traffic symbols and two or more either full length or shortpilot symbols. The short pilot symbols are generally spaced apart fromone another by at least one traffic symbol, and will have a Fouriertransform length that is less than the Fourier transform length of anygiven traffic symbol. In operation, multiple transmitters will generatepilot information and modulate the pilot information onto sub-carriersof the pilot symbols in an orthogonal manner. To maintain orthogonality,each transmitter may use different sub-carriers within the time andfrequency domain, which is encompassed by the pilot symbols within thetransmit time interval. Alternatively, each transmitter may uniquelyencode the pilot information using a unique code division multiplexedcode and modulate the encoded pilot information onto common sub-carriersof the pilot symbols.

Certain transmitters may have multiple transmission paths andcorresponding antennas wherein each transmission path or antenna isassociated with unique pilot information, which is modulated onto thesub-carriers of the pilot symbols in an orthogonal manner. Again,orthogonality may be maintained by using different sub-carriers for eachtransmission path or antenna for each transmitter. Alternatively, thepilot information may be encoded and modulated onto common sub-carriers.When multiple transmission paths or antennas are employed, orthogonalityis maintained among the transmission paths as well as amongtransmitters.

Data information may be modulated onto the sub-carriers of the trafficsymbols, and all or certain sub-carriers of the traffic symbols may beshared by different transmitters as well as different transmission pathsof a given transmitter. Further, sounding pilots may be provided on thepilot or short pilot symbols in addition to the pilot information.Different sub-carriers may be used for sounding pilots and pilotinformation. If the sounding pilots are uniquely encoded, commonsub-carriers of the short pilot symbols may be used. Generally, trafficinformation is not modulated on the pilot or short pilot symbols.

Those skilled in the art will appreciate the scope of the presentinvention and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a block representation of a wireless communication environmentaccording to one embodiment of the present invention.

FIG. 2 is a block representation of a base station according to oneembodiment of the present invention.

FIG. 3 is a block representation of a user element according to oneembodiment of the present invention.

FIG. 4 is a block representation of a wireless communication environmentproviding a first space-time coding scheme according to one embodimentof the present invention.

FIG. 5 is a block representation of a wireless communication environmentproviding a second space-time coding scheme according to one embodimentof the present invention.

FIG. 6 is a block representation of a wireless communication environmentproviding third space-time coding scheme according to one embodiment ofthe present invention.

FIG. 7 is a block representation of a wireless communication environmentproviding a fourth space-time coding scheme according to one embodimentof the present invention.

FIG. 8A is a more detailed logical representation of a transmissionarchitecture, such as that of a user element, having multipletransmission paths and antennas according to one embodiment of thepresent invention.

FIG. 8B is a more detailed logical representation of a transmissionarchitecture, such as that of a user element, having a singletransmission path and antenna according to one embodiment of the presentinvention.

FIG. 9 is a more detailed logical representation of a receiverarchitecture, such as that of a base station, having a multiple receivepaths and antennas according to one embodiment of the present invention.

FIG. 10A illustrates a transmit time interval.

FIG. 10B illustrates division of a pilot symbol into short pilot symbolsin the time domain according to one embodiment of the present invention.

FIG. 10C illustrates a transmit time interval incorporating two shortpilot symbols according to a first embodiment.

FIG. 10D illustrates a transmit time interval incorporating two shortpilot symbols according to a second embodiment.

FIG. 10E illustrates a transmit time interval incorporating three shortpilot symbols according to a third embodiment.

FIGS. 11A and 11B illustrate two different pilot signal schemesaccording to a first embodiment of the present invention.

FIGS. 12A and 12B illustrate two different pilot signal schemesaccording to a second embodiment of the present invention.

FIGS. 13A and 13B illustrate two different pilot signal schemesaccording to a third embodiment of the present invention.

FIGS. 14A and 14B illustrate two different pilot signal schemesaccording to a fourth embodiment of the present invention.

FIGS. 15A and 15B illustrate two different pilot signal schemesaccording to a fifth embodiment of the present invention.

FIGS. 16A and 16B illustrate two different pilot signal schemesaccording to a sixth embodiment of the present invention.

FIGS. 17A and 17B illustrate two different pilot signal schemesaccording to a seventh embodiment of the present invention.

FIGS. 18A and 18B illustrate two different pilot signal schemesaccording to an eighth embodiment of the present invention.

FIGS. 19A and 19B illustrate two different pilot signal schemesaccording to a ninth embodiment of the present invention.

FIGS. 20A and 20B illustrate two different pilot signal schemesaccording to a tenth embodiment of the present invention.

FIGS. 21A and 21B illustrate two different pilot signal schemesaccording to an eleventh embodiment of the present invention.

FIGS. 22A and 22B illustrate two different pilot signal schemesaccording to a twelfth embodiment of the present invention.

FIGS. 23A and 23B illustrate two different pilot signal schemesaccording to a thirteenth embodiment of the present invention.

FIG. 24 illustrates a pilot signal scheme according to a fourteenthembodiment of the present invention.

FIG. 25 illustrates a pilot signal scheme according to a fifteenthembodiment of the present invention.

FIG. 26 illustrates a pilot signal scheme according to a sixteenthembodiment of the present invention.

FIG. 27 illustrates a pilot signal scheme according to a seventeenthembodiment of the present invention.

FIG. 28 illustrates a pilot signal scheme according to a eighteenthembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the invention and illustratethe best mode of practicing the invention. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the invention and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

With reference to FIG. 1, a basic wireless communication environment isillustrated. A base station controller (BSC) 10 controls wirelesscommunications within multiple cells 12, which are served bycorresponding base stations (BS) 14. Each base station 14 facilitatescommunications with user elements 16, which are within the cell 12associated with the corresponding base station 14. For the presentinvention, the base stations 14 include multiple antennas to providespatial diversity for communications. The user elements 16 may or maynot have multiple antennas, depending on the implementation of thepresent invention.

With reference to FIG. 2, a base station 14 configured according to oneembodiment of the present invention is illustrated. The base station 14generally includes a control system 20, a baseband processor 22,transmit circuitry 24, receive circuitry 26, multiple antennas 28, and anetwork interface 30. The receive circuitry 26 receives radio frequencysignals through the antennas 28 bearing information from one or moreremote transmitters provided by user elements 16. Preferably, a lownoise amplifier and a filter (not shown) cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs). Thereceived information is then sent across a wireless network via thenetwork interface 30 or transmitted to another user element 16 servicedby the base station 14. The network interface 30 will typically interactwith the base station controller 10 and a circuit-switched networkforming a part of a wireless network, which may be coupled to the publicswitched telephone network (PSTN).

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of the control system 20, andencodes the data for transmission. The encoded data is output to thetransmit circuitry 24, where it is modulated by a carrier signal havinga desired transmit frequency or frequencies. A power amplifier (notshown) will amplify the modulated carrier signal to a level appropriatefor transmission, and deliver the modulated carrier signal to theantennas 28 through a matching network (not shown). The multipleantennas 28 and the replicated transmit and receive circuitries 24, 26provide spatial diversity. Modulation and processing details aredescribed in greater detail below.

With reference to FIG. 3, a user element 16 configured according to oneembodiment of the present invention is illustrated. Similarly to thebase station 14, the user element 16 will include a control system 32, abaseband processor 34, transmit circuitry 36, receive circuitry 38,antenna 40, and user interface circuitry 42. The receive circuitry 38receives radio frequency signals through the antenna 40 bearinginformation from one or more base stations 14. Preferably, a low noiseamplifier and a filter (not shown) cooperate to amplify and removebroadband interference from the signal for processing. Downconversionand digitization circuitry (not shown) will then downconvert thefiltered, received signal to an intermediate or baseband frequencysignal, which is then digitized into one or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations, as will be discussed in greater detail below. Thebaseband processor 34 is generally implemented in one or more digitalsignal processors (DSPs) and application specific integrated circuits(ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antenna 40 through a matching network(not shown). In select embodiments, multiple antennas 40 and replicatedtransmit and receive circuitries 36, 38 provide spatial diversity.

The present invention supports MIMO communications between base stations14 and user elements 16 that have multiple transmission paths andcorresponding antennas 40. Additionally, virtual MIMO communications aresupported between base stations 14 and multiple user elements 16, atleast one of which only has a single transmission path and antenna 40.In this case, the multiple user elements 16 cooperate to transmit datato the base station 14 to emulate MIMO communications.

MIMO communications generally employ some form of space-time coding onthe data to be transmitted to enable the data to be transmitted usingshared transmission resources. The particular space-time coding employeddictates what data is to be transmitted over a given one of the antennasas well as when the data is to be transmitted using the sharedresources. Popular types of space-time coding include spatialmultiplexing (SM) and space-time diversity (STD). Spatial multiplexingrelates to transmitting different data from different antennas where thesame data is not transmitted from different antennas. Spatialmultiplexing is used to increase throughput or transmission rates in thepresent of favorable channel conditions. Space-time diversity relates totransmitting the same data over different antennas, often at differenttimes. The inherent redundancy of spatial multiplexing increases therobustness of communications under challenging channel conditions or fordata requiring additional robustness at the expense of transmissionrates.

In one embodiment of the present invention, a single carrier frequencydivision multiple access (SC-FDM) technique is used for transmissions.Other multiple access technologies, such as orthogonal frequencydivision multiple access (OFDM) techniques may also be used with thepresent invention. Providing a MIMO architecture enabling multipletransmission paths can increase channel capacity by allowing multipleusers to share the same channels, increase data rates, or a combinationthereof. Further information regarding space-time diversity and specialmultiplexing is provided in commonly owned and assigned U.S. patentapplication Ser. No. 09/977,540 filed Oct. 15, 2001, Ser. No. 10/251,935filed Sep. 20, 2002, Ser. No. 10/261,739 filed Oct. 1, 2002, and Ser.No. 10/263,268 filed Oct. 2, 2002, the disclosures of which areincorporated herein by reference in their entireties.

With reference to FIG. 4, a MIMO communication environment is depictedwherein a user element 16M, which has two antennas 40, uses MIMOcommunications for uplink transmissions to the base station 14. The basestation 14 has at least two antennas 28. As illustrated, the MIMOcommunications may employ spatial multiplexing where different data istransmitted from each antenna 40 of user element 16M, or space-timediversity where the same data is transmitted from each antenna 40 atdifferent times.

With reference to FIG. 5, a MIMO communication environment is depictedwherein different user elements 16S, which have only one antenna 40each, use collaborative MIMO communications for uplink transmissions tothe base station 14. The base station 14 has at least two antennas 28.As illustrated, the MIMO communications employ spatial multiplexingwhere different data is transmitted from the different user elements 16Musing the same transmission resources. Additional information regardingcollaborative, or virtual, MIMO communications is provided in commonlyowned and assigned U.S. application Ser. No. 10/321,999, filed Dec. 16,2002, the disclosure of which is incorporated herein by reference in itsentirety.

With reference to FIG. 6, a MIMO communication environment is depictedwherein different user elements 16M, which have two antennas 40 each,use collaborative MIMO communications for uplink transmissions to thebase station 14. The base station 14 has at least two antennas 28. Asillustrated, the MIMO communications from each of the user elements 16Memploy space-time diversity, wherein the same data is transmitted fromthe different antennas 40 at different times for each of the userelements 16M using the same transmission resources. However, differentdata is being transmitted from each user element 16M. As such, the basestation 14 may process the received signals as spatially multiplexedsignals.

With reference to FIG. 7, a MIMO communication environment is depictedwherein two user elements 16S and one user element 16M use collaborativeMIMO communications for uplink transmissions to the base station 14. Theuser elements 16S have one antenna 40 each while the user element 16Mhas two antennas 40. The base station 14 has at least two antennas 28.As illustrated, the MIMO communications from the user element 16M employspace-time diversity where the same data is transmitted from eachantenna 40 of the user element 16M at different times. The MIMOcommunications from each of the user elements 16S employ spatialmultiplexing where different data is transmitted from each antenna 40 ofthe mobile terminals 16S. Notably, since the data transmitted from userelement 16M is different than that transmitted for either of userelements 16S, each of the user elements 16S and the user element 16M arecollaborating to effectively provide spatial multiplexing with respectto one another. This is the case even though user element 16M is usingspace-time diversity for its data transmissions.

Turning now to FIGS. 8A and 8B, a logical transmission architecture forSC-FDM communications is provided for a multiple antenna embodiment anda single antenna embodiment. For clarity and conciseness, only selectfunctions are illustrated, even though other functions are described toprovide context. With particular reference to FIG. 8A, data to betransmitted is provided to a symbol mapping function 44, whichsystematically maps the bits of the data into corresponding symbolsdepending on a chosen baseband modulation technique. As an example, thebaseband modulation may include a form of Quadrature AmplitudeModulation (QAM) or Quadrature Phase Shift Key (QPSK) modulation.

At this point, groups of bits representing the data to be transmittedhave been mapped into symbols representing locations in an amplitude andphase constellation and are ready to be modulated. For SC-FDMmodulation, the symbols are presented to a Fast Fourier Transform (FFT)pre-processor function 46, which operates to provide some form ofdiscrete FFT on the symbols. The FFT data is then presented to aspace-time code (STC) encoder 48 that will encode the FFT data accordingto the desired space-time encoding technique, such as spatialmultiplexing or space-time diversity. The resultant space-time encodeddata is then presented to the respective sub-carrier mapping function 50in light of the space-time encoding. The sub-carrier mapping function 50is tasked with mapping the space-time encoded FFT data to appropriatesub-carriers in the time-frequency continuum provided by the SC-FDMresource, which is described below in greater detail. For space-timediversity encoding, the space-time encoded FFT data will be presented tothe different sub-carrier mapping functions 50 at different times. Forspatial multiplexing, different space-time encoded FFT data is presentedto different sub-carrier mapping functions 50. The sub-carrier mappingessentially maps samples of the space-time encoded FFT data to anappropriate input of one of the inverse FFT (IFFT) processors 52, whichoperate on the space-time encoded FFT data using an inverse discreteFourier transform (IDFT) or like processing to provide an InverseFourier Transform.

Each of the resultant signals is then up-converted in the digital domainto an intermediate frequency and converted to an analog signal viacorresponding digital up-conversion (DUC) circuitry anddigital-to-analog (D/A) conversion circuitry (not shown). The resultantanalog signals are then simultaneously modulated at the desired RFfrequency, amplified, and transmitted via RF circuitry and the antennas40.

Notably, the transmitted data may include pilot signals, which werepreviously assigned by the base station 14. The base station 14, whichis discussed in detail below, may use the pilot signals for channelestimation and interference suppression, as well as to identify the userelement 16. The pilot symbols are created by a pilot symbol generationfunction 54 and presented to the different sub-carrier mapping functions50, which will map the pilot symbols to appropriate sub-carriers alongwith the space-time encoded FFT data. As such, the IFFT processors 52effectively modulate the FFT data and the pilot information onto desiredsub-carriers of an SC-FDM signal.

With particular reference to FIG. 8B, data to be transmitted is providedto the symbol mapping function 44, which systematically maps the bits ofthe data into corresponding symbols depending on a chosen basebandmodulation technique. For SC-FDM modulation, the symbols are presentedto the FFT pre-processor function 46, which operates to provide someform of an FFT on the symbols. The resultant FFT data is then presentedto the sub-carrier mapping function 50, which will mapping the FFT datato appropriate sub-carriers in the time-frequency continuum provided bythe SC-FDM resource. The sub-carrier mapping essentially maps samples ofthe FFT data to an appropriate input of one of the IFFT processors 52,which operate on the FFT data using IDFT or like processing to providean Inverse Fourier Transform.

Each of the resultant signals is then up-converted in the digital domainto an intermediate frequency and converted to an analog signal viacorresponding digital up-conversion (DUC) circuitry anddigital-to-analog (D/A) conversion circuitry. The resultant analogsignals are then simultaneously modulated at the desired RF frequency,amplified, and transmitted via RF circuitry and the antenna 40.

As noted above, the transmitted data may include pilot signals, whichwere previously assigned by the base station 14. The base station 14 mayuse the pilot signals for channel estimation and interferencesuppression, as well as to identify the user element 16. The pilotsymbols are created by a pilot generation function 54 and presented tothe different sub-carrier mapping function 50, which will map the pilotsymbols to appropriate sub-carriers along with the FFT data. As such,the IFFT processors 52 effectively modulate the FFT data and the pilotsymbols into desired sub-carriers of the SC-FDM signal.

Those skilled in the art will recognize that the order of the FFT andIFFT functions of the pre-processor and modulation blocks may bereversed. For example, the symbols may be presented to an IFFTpre-processor function, which operates to provide some form of an IFFTon the symbols. The resultant IFFT data is then presented to thesub-carrier mapping function 50, which will map the IFFT data toappropriate sub-carriers in the time-frequency continuum provided by theSC-FDM resource. The sub-carrier mapping essentially maps samples of theIFFT data to an appropriate input of one of FFT processors, whichoperate on the IFFT data using an FFT or like processing to provide aFourier Transform. On the receive side, the signals are initiallypresented to an IFFT and then to an FFT to recover the transmitted data.

Turning now to FIG. 9, a logical receiver architecture for SC-FDMcommunications is provided for a multiple antenna embodiment. Forclarity and conciseness, only select functions are illustrated, eventhough other functions are described to provide context. Upon arrival ofthe transmitted signals at each of the antennas 28, the respectivesignals are demodulated and amplified by corresponding RF circuitry. Forthe sake of conciseness and clarity, only one of the multiple receivepaths in the receiver architecture is described. Analog-to-digital (A/D)conversion and downconversion circuitry (DCC) (not shown) digitizes anddownconverts the analog signal for digital processing. The digitizedsignal is fed to a corresponding multiple access demodulation function,such as the FFT processor 56. Using a discrete FFT or the like, the FFTprocessor 56 will recover (space-time encoded) FFT data corresponding tothat which was modulated in the incoming signal received at acorresponding antenna 28 for each receive path.

A channel estimation function 60 for each receive path provides channelresponses corresponding to channel conditions for use by an STC decoder58. The FFT data from the incoming signal and channel estimates for eachreceive path are provided to the STC decoder 58. The channel estimatesprovide sufficient channel response information to allow the STC decoder58 to decode the FFT data according to STC encoding used by the userelements 16.

The decoded FFT data is then presented to an IFFT post-processorfunction 62, which provides an inverse discrete FFT (IDFT) or the likeon the FFT data to recover the transmitted symbols from each userelement 16. The symbols are then demapped by the symbol de-mappingfunction 64 to recover the corresponding data transmitted by the userelements 16.

In operation, the base station 14 initially identifies MIMO-capable userelements 16 or a sub-set of user elements 16 to collaborate with oneanother during uplink transmissions. Next, the base station 14 willassign shared resources to each of the cooperating user elements 16 viadownlink channels. For an SC-FDM embodiment, the shared resources mayinclude a common sub-carrier block, which is the group of sub-carriersin the time-frequency domain that the user elements 16 will use fortransmission. Each of the participating user elements 16 may transmitinformation using the common sub-carrier block at the same time. Next,the base station 14 may assign user-specific resources to the individualuser elements 16 in the group via the downlink channels. Numerousexamples of shared and user-specific resources are provided furtherbelow.

Once shared and any user-specific resources are assigned, each userelement 16 in the cooperating group will transmit data to the basestation 14 in synchronized time slots, referred to as transmit timeintervals, using the appropriate resources. The base station 14 willreceive the transmitted signals from the user elements 16 and extractthe pilot signals for each of the user elements 16 to help identify theuser elements 16 transmitting information, as well as estimate thechannel conditions for the MIMO channel. Finally, the base station 14will decode the received signals to extract the data or informationtransmitted by each of the participating user elements 16, as describedabove.

With reference to FIG. 10A, a transmit time interval (TTI) in the timedomain is illustrated. The TTI is broken into seven sub-intervals duringwhich different traffic symbols are transmitted. The traffic symbols maycorrespond to FFT data, which may or may not be space-time encoded. ForSC-FDM and related FDM techniques, each sub-interval is associated withnumerous sub-carriers on which samples corresponding to the symbol dataare concurrently modulated. Sub-intervals having the same lengthgenerally have the same number of available sub-carriers. Thus, theinterval for the pilot symbol (PS) may be associated with the samenumber of sub-carriers as the sub-intervals for the traffic symbols(TS-1 through TS-6). Generally, traffic information is not carried onthe pilot symbols, and pilot information is not carried on the trafficsymbols.

In one embodiment, the pilot symbol is effectively shortened withrespect to the traffic symbols and presented during differentsub-intervals in the TTI. As illustrated in FIG. 10B, the pilot symbolof FIG. 10A may be divided into two short pilot symbols (SPS-1 andSPS-2), which are provided during two shortened sub-intervals atdifferent times during the TTI in FIG. 10C. An alternative placement forthe shortened pilot symbols is provided in FIG. 10D. For the followingdescription, short pilot symbols are used as examples; however, pilotsymbols having the same effective size or length as the traffic symbolsmay be employed.

Shortening a symbol reduces the length of the corresponding sub-intervaland reduces the number of available sub-carriers for the symbol. Therelative length of a symbol, and thus the corresponding sub-interval, iscontrolled by the relative length or number of inputs to an IFFT oroutputs of an FFT. For transmitting a traffic symbol or pilot symbol ofthe same length as a traffic symbol, N samples corresponding to thetraffic data may be presented to the IFFT to provide N sub-carriers. Fortransmitting short pilot symbols, the N/M (where M is greater than 1)samples corresponding to the short pilot symbol may be presented to theIFFT to provide N/M sub-carriers. For example, 512 samples for a trafficsymbol may be presented to the input of the IFFT to be modulated onto512 sub-carriers (N=512). A short pilot symbol may be represented by 256samples, which are presented to the input of the IFFT to be modulatedonto 256 sub-carriers (M=2). For the present invention, short pilotsymbols having an FFT length less than the traffic symbols may bedistributed throughout the TTI. In one embodiment, the combined lengthof the short pilot symbols corresponds to the length of one trafficsymbol. FIGS. 10C and 10D provide examples where the two short pilotsymbols (and corresponding sub-intervals) in the TTI are each one-halfthe length of a traffic symbol. FIG. 10E provides an example where threeshort pilot symbols (and corresponding sub-intervals) in the TTI areeach one-third the length of a traffic symbol.

By using multiple short pilot symbols throughout the TTI, the density ofpilot information is increased in the time domain and decreased in thefrequency domain as will become more apparent below. By distributing thepilot information throughout the TTI, better channel estimates may bederived over the entire TTI. As a result, demodulation is more accurate,especially for fast-moving user elements 16. This is particularlybeneficial in uplink communications because channel estimates from oneTTI may not be available or applicable for a subsequent TTI, sincedifferent user elements 16 may be using the resources in the subsequentTTI.

For FIGS. 11A through 27, various pilot signal schemes are illustratedfor regular and collaborative MIMO in an SC-FDM environment. Certainpilot schemes are for a given user element 16 that has multiple antennas40, while others are for multiple user elements 16 that have one or moreantennas 40. As such, the illustrated pilot schemes often represent thepilot and traffic information of multiple user elements 16 for a givenTTI. Each pilot signal scheme employs short pilot symbols anddistributes the short pilot symbols along the TTI. Different figuresprovide short pilot symbols of different lengths; however, certainembodiments may employ traffic symbols of the same size or length as thepilot symbols. In each illustrated scenario, the short pilot symbols areeither one-half or one-quarter of the FFT length of the traffic symbols.Those skilled in the art will recognize that the short pilot symbols mayhave other FFT lengths. For clarity in the following descriptions, thepilot information used for transmission via different antennas from agiven user elements 16 is referenced as being for the specific antennas40.

Each figure provides the sub-carrier mapping for pilot information forthe short pilot symbols and data for the traffic part of the frequencydomain is illustrated for a given TTI. Each circle represents asub-carrier for either a short pilot or traffic symbol, either of whichmay be used by one or more user elements 16 at any given time. Eachcolumn of circles represents the sub-carriers associated with a givenshort pilot symbol or traffic symbol. In each scenario, there are sixtraffic symbols and the entire TTI is effectively the FFT length ofseven traffic symbols. Most of the remaining portion of the TTI isfilled with multiple short pilot symbols.

Notably, the time axis of the frequency domain graphs is not linear. Inessence, the short pilot symbols require a shorter time period withinthe TTI relative to the traffic symbols. Further, the short pilotsymbols have fewer sub-carriers than the traffic symbols. The relativeFFT lengths of the short pilot symbols (SPS) and the traffic symbols(TS) are identified on each figure, as either SPS=½ TS or SPS=¼ TS. Assuch, the sub-interval for an SPS may be approximately or exactlyone-half or one-quarter of the sub-interval for the traffic symbol,depending on the example and after any prefixes or other signaling havebeen removed. Accordingly, the number of available sub-carriers for theshort pilot symbols is one-half or one-quarter of the number ofsub-carriers available for the traffic symbols.

With particular reference to FIGS. 11A and 11B, two different pilotschemes are provided for a single user element 16 that can provide MIMOcommunications via two antennas, which are referenced as Ant-0 andAnt-1. As illustrated, pilot information associated with both antennasAnt-0 and Ant-1 is provided on two short pilot symbols, which arelocated on either end of the TTI. The short pilot symbols have an FFTlength that is one-half of that of the traffic symbols. The samesub-carriers for a given traffic symbol may be used by each antennaAnt-0 and Ant-1 to transmit data at any given time. The six trafficsymbols are used for space-time coded information, which may representthe space-time division or spatial multiplexing of FFT data. In thisembodiment, the pilot information for each of the antennas Ant-0 andAnt-1 is orthogonally mapped onto the sub-carriers of both of the shortpilot symbols. Given the orthogonal nature of the mapping, any onesub-carrier of the short pilot symbols will have pilot information foronly one of the two antennas Ant-0 and Ant-1.

For FIGS. 12A and 12B, two different pilot schemes are provided for asingle user element 16 that can provide MIMO communications via the twoantennas 40, Ant-0 and Ant-1. As illustrated, pilot informationassociated with both antennas Ant-0 and Ant-1 are provided on threeshort pilot symbols, which are located on either end and in the middleof the TTI. The short pilot symbols have an FFT length that isone-quarter that of the traffic symbols. The remaining portion of theTTI may be filled with prefix or other signaling information. The sixtraffic symbols are used for transmitting traffic data (data). The samesub-carriers for a given traffic symbol may be used by each antennaAnt-0 and Ant-1 to transmit data at any given time. In this embodiment,the pilot information for each of the antennas Ant-0 and Ant-1 isorthogonally mapped onto the sub-carriers of the short pilot symbols.Given the orthogonal nature of the mapping, any one sub-carrier of theshort pilot symbols will have pilot information for only one of the twoantennas Ant-0 and Ant-1.

For FIGS. 13A and 13B, two different pilot schemes are provided for asingle user element 16 that can provide MIMO communications via fourantennas 40, which are referenced as Ant-0, Ant-1, Ant-2, and Ant-3. Asillustrated, pilot information associated with each antenna Ant-0,Ant-1, Ant-2, and Ant-3 are provided on three short pilot symbols, whichare located on either end and in the middle of the TTI. The short pilotsymbols have an FFT length that is one-quarter that of the trafficsymbols. The remaining portion of the TTI may be filled with prefix orother signaling information. The six traffic symbols are used fortransmitting traffic data (data). The same sub-carriers for a giventraffic symbol may be used by each antenna Ant-0, Ant-1, Ant-2, andAnt-3 to transmit data at any given time. In this embodiment, the pilotinformation for each of the antennas Ant-0, Ant-1, Ant,-2, and Ant-3 isorthogonally mapped onto the sub-carriers of the short pilot symbols.Given the orthogonal nature of the mapping, any one sub-carrier of theshort pilot symbols will have pilot information for only one of the fourantennas Ant-0, Ant-1, Ant-2, and Ant-3.

For FIGS. 14A and 14B, two different pilot schemes are provided for asingle user element 16 that can provide MIMO communications via fourantennas 40, which are referenced as Ant-0, Ant-1, Ant-2, and Ant-3. Asillustrated, pilot information associated with each antenna Ant-0,Ant-1, Ant-2, and Ant-3 are provided on two short pilot symbols, whichare located on either end of the TTI. The short pilot symbols have anFFT length that is one-half of that of the traffic symbols. Anyremaining portions of the TTI may be filled with prefix or othersignaling information. The six traffic symbols are used for transmittingtraffic data (data). The same sub-carriers for a given traffic symbolmay be used by each antenna Ant-0, Ant-1, Ant-2, and Ant-3 to transmitdata at any given time. In this embodiment, the pilot information foreach of the antennas Ant-0, Ant-1, Ant,-2, and Ant-3 is orthogonallymapped onto the sub-carriers of the short pilot symbols. Given theorthogonal nature of the mapping, any one sub-carrier of the short pilotsymbols will have pilot information for only one of the four antennasAnt-0, Ant-1, Ant-2, and Ant-3.

For FIGS. 15A and 15B, two different pilot schemes are provided for twouser elements 16, each which can provide MIMO communications via twoantennas 40. The two user elements 16 are referenced as UE-1 and UE-2.The two antennas for UE-1 are referenced as Ant-0/UE-1 and Ant-1/UE-1.The two antennas for UE-2 are referenced as Ant-0/UE-2 and Ant-1/UE-2.As illustrated, pilot information associated with each user element UE-1and UE-2, and in particular with antenna Ant-0/UE-1, Ant-1/UE-1,Ant-0/UE-2, and Ant-1/UE-2 are provided on three short pilot symbols,which are located on either end and in the middle of the TTI. The shortpilot symbols have an FFT length that is one-quarter of that of thetraffic symbols. The remaining portion of the TTI may be filled withprefix or other signaling information. The six traffic symbols are usedfor transmitting traffic data (data) for each of the user elements UE-1and UE-2. The same sub-carriers for a given traffic symbol may be usedby each antenna Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 totransmit data at any given time. In this embodiment, the pilotinformation for each of the antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2,and Ant-1/UE-2 is orthogonally mapped onto the sub-carriers of the shortpilot symbols. Given the orthogonal nature of the mapping, any onesub-carrier of the short pilot symbols will have pilot information foronly one of the four antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, andAnt-1/UE-2. Further, the traffic data for both user elements UE-1 andUE-2 are transmitted on sub-carriers for each of the traffic symbols.However, the user elements UE-1 and UE-2 are allocated uniquesub-carriers for each traffic symbol. Thus, only one of the userelements UE-1 and UE-2 may use a given sub-carrier for transmittingtraffic data from antenna Ant-0 and Ant-1 at the same time. The givensub-carrier will not be used by the other of the user elements UE-1 andUE-2.

For FIGS. 16A and 16B, two different pilot schemes are provided for twouser elements 16, each which can provide MIMO communications via the twoantennas 40. The two user elements 16 are referenced as UE-1 and UE-2.The two antennas for UE-1 are referenced as Ant-0/UE-1 and Ant-1/UE-1.The two antennas for UE-2 are referenced as Ant-0/UE-2 and Ant-1/UE-2.As illustrated, pilot information associated with each user element UE-1and UE-2, and in particular with antenna Ant-0/UE-1, Ant-1/UE-1,Ant-0/UE-2, and Ant-1/UE-2 are provided on two short pilot symbols,which are located on either end of the TTI. The short pilot symbols havean FFT length that is one-half of that of the traffic symbols. Theremaining portion of the TTI may be filled with prefix or othersignaling information. The six traffic symbols are used for transmittingtraffic data (data) for each of the user elements UE-1 and UE-2. Thesame sub-carriers for a given traffic symbol may be used by each antennaAnt-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 to transmit data atany given time. In this embodiment, the pilot information for each ofthe antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 isorthogonally mapped onto the sub-carriers of the short pilot symbols.Given the orthogonal nature of the mapping, any one sub-carrier of theshort pilot symbols will have pilot information for only one of the fourantennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2. Further,the traffic data for both user elements UE-1 and UE-2 are transmitted onsub-carriers for each of the traffic symbols. However, the user elementsUE-1 and UE-2 are allocated unique sub-carriers for each traffic symbol.Thus, only one of the user elements UE-1 and UE-2 may use a givensub-carrier for transmitting traffic data from antenna Ant-0 and Ant-1at the same time. The given sub-carrier will not be used by the other ofthe user elements UE-1 and UE-2.

For FIGS. 17A and 17B, two different pilot schemes are provided for twouser elements UE-1 and UE2 that each have one antenna 40 and arecollaborating to effect MIMO communications. As illustrated, pilotinformation associated with both user elements UE-1 and UE-2 areprovided on three short pilot symbols, which are located on either endand in the middle of the TTI. The short pilot symbols have an FFT lengththat is one-quarter of that of the traffic symbols. The remainingportion of the TTI may be filled with prefix or other signalinginformation. The six traffic symbols are used for transmitting trafficdata (data) of the user elements UE-1 and UE-2. Any given sub-carriermay be assigned solely to one of the user elements UE-1 and UE-2 orassigned to both of the user elements UE-1 and UE-2 for transmittingtraffic data at any given time. In this embodiment, the pilotinformation for each of the antennas of user elements UE-1 and UE-2 isorthogonally mapped onto the sub-carriers of the short pilot symbols.Given the orthogonal nature of the mapping, any one sub-carrier of theshort pilot symbols will have pilot information for only one of the twouser elements UE-1 and UE-2.

For FIGS. 18A and 18B, two different pilot schemes are provided for twouser elements UE-1 and UE2 that each have one antenna 40 and arecollaborating to effect MIMO communications. As illustrated, pilotinformation associated with both user elements UE-1 and UE-2 areprovided on two short pilot symbols, which are located on either end ofthe TTI. The short pilot symbols have an FFT length that is one-half ofthat of the traffic symbols. Any remaining portion of the TTI may befilled with prefix or other signaling information. The six trafficsymbols are used for transmitting traffic data (data) of the userelements UE-1 and UE-2. Any given sub-carrier may be assigned solely toone of the user elements UE-1 and UE-2 or assigned to both of the userelements UE-1 and UE-2 for transmitting traffic data at any given time.In this embodiment, the pilot information for each of the antennas ofuser elements UE-1 and UE-2 is orthogonally mapped onto the sub-carriersof the short pilot symbols. Given the orthogonal nature of the mapping,any one sub-carrier of the short pilot symbols will have pilotinformation for only one of the two user elements UE-1 and UE-2.

For FIGS. 19A and 19B, two different pilot schemes are provided for twouser elements 16, each of which can provide MIMO communications via twoantennas 40. The two user elements 16 are referenced as UE-1 and UE-2.The two antennas for UE-1 are referenced as Ant-0/UE-1 and Ant-1/UE-1.The two antennas for UE-2 are referenced as Ant-0/UE-2 and Ant-1/UE-2.As illustrated, pilot information associated with each user element UE-1and UE-2, and in particular with antenna Ant-0/UE-1, Ant-1/UE-1,Ant-0/UE-2, and Ant-1/UE-2 are provided on three short pilot symbols,which are located on either end and in the middle of the TTI. The shortpilot symbols have an FFT length that is one-quarter of that of thetraffic symbols. The remaining portion of the TTI may be filled withprefix or other signaling information. The six traffic symbols are usedfor transmitting traffic data (data) for each of the user elements UE-1and UE-2. The same sub-carriers for a given traffic symbol may be usedby each antenna Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 totransmit data at any given time. In this embodiment, the pilotinformation for each of the antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2,and Ant-1/UE-2 is orthogonally mapped onto the sub-carriers of the shortpilot symbols. Given the orthogonal nature of the mapping, any onesub-carrier of the short pilot symbols will have pilot information foronly one of the four antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, andAnt-1/UE-2. The traffic data for both user elements UE-1 and UE-2 may betransmitted on the same sub-carriers of the traffic symbols at any giventime. Thus, both of the user elements UE-1 and UE-2 may use a givensub-carrier for transmitting traffic data from antenna Ant-0 and Ant-1at the same time.

For FIGS. 20A and 20B, two different pilot schemes are provided for twouser elements 16, each which can provide MIMO communications via twoantennas 40. The two user elements 16 are referenced as UE-1 and UE-2.The two antennas for UE-1 are referenced as Ant-0/UE-1 and Ant-1/UE-1.The two antennas for UE-2 are referenced as Ant-0/UE-2 and Ant-1/UE-2.As illustrated, pilot information associated with each user element UE-1and UE-2, and in particular with antenna Ant-0/UE-1, Ant-1/UE-1,Ant-0/UE-2, and Ant-1/UE-2 are provided on two short pilot symbols,which are located on either end of the TTI. The short pilot symbols havean FFT length that is one-half of that of the traffic symbols. Theremaining portion of the TTI may be filled with prefix or othersignaling information. The six traffic symbols are used for transmittingtraffic data (data) for each of the user elements UE-1 and UE-2. Thesame sub-carriers for a given traffic symbol may be used by each antennaAnt-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 to transmit data atany given time. In this embodiment, the pilot information for each ofthe antennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2 isorthogonally mapped onto the sub-carriers of the short pilot symbols.Given the orthogonal nature of the mapping, any one sub-carrier of theshort pilot symbols will have pilot information for only one of the fourantennas Ant-0/UE-1, Ant-1/UE-1, Ant-0/UE-2, and Ant-1/UE-2. Further,the traffic data for both user elements UE-1 and UE-2 are transmitted onsub-carriers for each of the traffic symbols. The traffic data for bothuser elements UE-1 and UE-2 may be transmitted on the same sub-carriersof the traffic symbols at any given time. Thus, both of the userelements UE-1 and UE-2 may use a given sub-carrier for transmittingtraffic data from antenna Ant-0 and Ant-1 at the same time.

For FIGS. 21A and 21B, two different pilot schemes are provided for fouruser elements 16 that each have one antenna 40 and are collaborating toeffect MIMO communications. The four user elements 16 are referenced asUE-1, UE-2, UE-3, and UE-4. As illustrated, pilot information associatedwith user elements UE-1, UE-2, UE-3, and UE-4 are provided on threeshort pilot symbols, which are located on either end and in the middleof the TTI. The short pilot symbols have an FFT length that isone-quarter of that of the traffic symbols. The remaining portion of theTTI may be filled with prefix or other signaling information. The sixtraffic symbols are used for transmitting traffic data (data) for eachof the user elements UE-1, UE-2, UE-3, and UE-4. The same sub-carriersfor a given traffic symbol may be used by user elements UE-1, UE-2,UE-3, and UE-4 to transmit data at any given time. In this embodiment,the pilot information for each of the user elements UE-1, UE-2, UE-3,UE-4 is orthogonally mapped onto the sub-carriers of the short pilotsymbols. Given the orthogonal nature of the mapping, any one sub-carrierof the short pilot symbols will have pilot information for only one ofthe user elements UE-1, UE-2, UE-3, and UE-4. Further, the traffic datafor user elements UE-1 and UE-2 are allocated certain sub-carriers foreach of the traffic symbols while traffic data for user elements UE-3and UE-4 are allocated different sub-carriers for each of the trafficsymbols. The user elements UE-1 and UE-2 may use an allocatedsub-carrier for transmitting traffic data at the same time. Userelements UE-3 and UE-4 may do the same. However, user elements UE-1 andUE-2 may not use the sub-carriers that are allocated to user elementsUE-3 and UE-4, and vice versa.

For FIGS. 22A and 22B, two different pilot schemes are provided for fouruser elements 16 that each have one antenna 40 and are collaborating toeffect MIMO communications. The four user elements 16 are referenced asUE-1, UE-2, UE-3, and UE-4. As illustrated, pilot information associatedwith user elements UE-1, UE-2, UE-3, and UE-4 are provided on two shortpilot symbols, which are located on either end of the TTI. The shortpilot symbols have an FFT length that is one-half of that of the trafficsymbols. The remaining portion of the TTI may be filled with prefix orother signaling information. The six traffic symbols are used fortransmitting traffic data (data) for each of the user elements UE-1,UE-2, UE-3, and UE-4. The same sub-carriers for a given traffic symbolmay be used by user elements UE-1, UE-2, UE-3, and UE-4 to transmit dataat any given time. In this embodiment, the pilot information for each ofthe user elements UE-1, UE-2, UE-3, UE-4 is orthogonally mapped onto thesub-carriers of the short pilot symbols. Given the orthogonal nature ofthe mapping, any one sub-carrier of the short pilot symbols will havepilot information for only one of the user elements UE-1, UE-2, UE-3,and UE-4. Further, the traffic data for user element UE-1 and UE-2 areallocated certain sub-carriers for each of the traffic symbols, whiletraffic data for user elements UE-3 and UE-4 are allocated differentsub-carriers for each of the traffic symbols. The user elements UE-1 andUE-2 may use an allocated sub-carrier for transmitting traffic data atthe same time. User elements UE-3 and UE-4 may do the same. However,user elements UE-1 and UE-2 may not use the sub-carriers that areallocated to user elements UE-3 and UE-4, and vice versa.

With the above embodiments, the sub-carriers for a given short pilotsymbol were not shared at any given time for different antennas 40 oruser elements 16. Once a sub-carrier of a short pilot symbol wasassigned pilot information for an antenna 40 or user element 16, a basestation 14 would not assign the sub-carrier for use by other antennas 40or user elements 16 at that time. With another embodiment of theinvention, the same sub-carrier may be used by different antennas 40 oruser elements 16 by employing code division multiplexing (CDM). Inessence, each antenna 40 or user element 16 is associated with a uniquecode, which is used to process the corresponding pilot information. Theencoded pilot information for different antennas 40 or user elements 16may then be assigned to the same sub-carriers. The encoding of the pilotinformation may take place in the pilot symbol generation function 54 ofthe transmitter architectures illustrated in FIGS. 8A and 8B.

For FIGS. 23A and 23B the pilot information is encoded using CDMtechniques and mapped to the same sub-carriers of the short pilotsymbols. For FIG. 23A, a pilot scheme is provided for two user elementsUE-1 and UE-2 that each have one antenna 40 and are collaborating toeffect MIMO communications. As illustrated, pilot information associatedwith both user elements UE-1 and UE-2 are provided on three short pilotsymbols, which are located on either end and in the middle of the TTI.The short pilot symbols have an FFT length that is one-quarter of thatof the traffic symbols. The remaining portion of the TTI may be filledwith prefix or other signaling information. The six traffic symbols areused for transmitting traffic data (data) of the user elements UE-1 andUE-2. Any given sub-carrier may be assigned solely to one of the userelements UE-1 and UE-2 or assigned to both of the user elements UE-1 andUE-2 for transmitting traffic data at any given time. In thisembodiment, the CDM encoded pilot information for each of the antennasfor user elements UE-1 and UE-2 are mapped onto the same sub-carriers ofthe short pilot symbols. Although pilot information for both userelements 16 are mapped on the same sub-carriers of the short pilotsymbols, the pilot information for each user element 16 is stillorthogonal due to the CDM encoding.

The pilot scheme provided in FIG. 23B is similar to that of FIG. 23A,except that the CDM encoded pilot information associated with both userelements UE-1 and UE-2 are provided on two short pilot symbols, whichare located on either end of the TTI. The short pilot symbols have anFFT length that is one-half of that of the traffic symbols. Again, theCDM encoded pilot information for each of the antennas for user elementsUE-1 and UE-2 are mapped onto the same sub-carriers of the short pilotsymbols.

Sounding pilots may be employed by user elements 16 to assist indetermining channel conditions. Sounding pilots are generally notmodulated with known data. With reference to FIG. 24, a pilot scheme isprovided for two user elements UE-1 and UE-2 that each have one antenna40 and are collaborating to effect MIMO communications. As illustrated,pilot information associated with both user elements UE-1 and UE-2 areprovided on two short pilot symbols, which are located on either end ofthe TTI. The short pilot symbols have an FFT length that is one-half ofthat of the traffic symbols. Any remaining portion of the TTI may befilled with prefix or other signaling information. The six trafficsymbols are used for transmitting traffic data (data) of the userelements UE-1 and UE-2. Any given sub-carrier may be assigned solely toone of the user elements UE-1 and UE-2 or assigned to both of the userelements UE-1 and UE-2 for transmitting traffic data at any given time.In this embodiment, the pilot information for each of the antennas userelements UE-1 and UE-2 is orthogonally mapped onto every other one ofthe sub-carriers of the short pilot symbols. Given the orthogonal natureof the mapping, these sub-carriers will have pilot information for onlyone of the two user elements UE-1 and UE-2. The remaining sub-carriersof the short pilot symbols may be used by user elements 16 other thanuser elements UE-1 and UE-2 to provide sounding pilots. These soundingpilots for each of the other user elements 16 may be mapped to uniquesub-carriers. Alternatively, the sounding pilots may be CDM encoded andmapped to common sub-carriers.

The pilot scheme in FIG. 25 is similar to that in FIG. 24, except thatthe pilot information for user elements UE-1 and UE-2 is CDM encoded andmapped to the same sub-carriers of the short pilot symbol. As such, halfof the sub-carriers in the short pilot symbols are allocated to CDMencode pilot information for user elements UE-1 and UE-2, while othersub-carriers of the short pilot symbols are allocated for soundingpilots for other user elements 16.

The pilot scheme of FIG. 26 is similar to that of FIG. 24, except thatall of the sub-carriers in the short pilot symbols are allocated to theuser elements UE-1 and UE-2 for pilot information and sounding pilots.These sub-carriers may also be used for sounding pilots by other userelements 16 in addition to user elements UE-1 and UE-2. The pilotinformation and the sounding information for the respective userelements UE-1 and UE-2 are CDM encoded to maintain orthogonality.

In FIG. 27, the sub-carriers of the short pilot symbols are broken intothree groups. The first group of sub-carriers is used by user elementsUE-1 and UE-2 for pilot information and sounding pilots. Thesesub-carriers may also be used for sounding pilots by other user elements16 in addition to user elements UE-1 and UE-2. The pilot information andthe sounding pilots are CDM encoded and allocated to the samesub-carriers. The second group of sub-carriers is used solely for pilotinformation (no sounding pilots) by user elements UE-1 and UE-2. Thepilot information is CDM encoded and allocated to the same sub-carriers.The third group of sub-carriers is allocated for sounding pilots foruser elements 16 other than user elements UE-1 and UE-2.

The pilot scheme of FIG. 28 is similar to that of FIG. 27, except thatthe sub-carriers of the short pilot symbols are broken into four groups.The first group of sub-carriers is used by user elements UE-1 and UE-2for pilot information and sounding pilots. These sub-carriers may alsobe used for sounding pilots by other user elements 16 in addition touser elements UE-1 and UE-2. The pilot information and the soundingpilots are CDM encoded and allocated to the same sub-carriers. Thesecond group of sub-carriers is used solely for pilot information (nosounding pilots) by user element UE-1. The third group of sub-carriersis used solely for pilot information (no sounding pilots) by userelement UE-2. The pilot information for groups two and three isallocated to the different sub-carriers. The fourth group ofsub-carriers is allocated for sounding pilots for user elements 16 otherthan user elements UE-1 and UE-2.

From the above, those skilled in the art will recognize that innumerableother pilot schemes that employ the concepts of the present inventionare possible. For example, the examples provided in FIGS. 23A through 27may be extended for mobile terminals 16 having multiple antennas 40 inaddition to the collaborative examples provided.

The pilot schemes are generally under the control of the base station14, which may instruct the user elements 16 being served by the basestation 14 to employ particular pilot schemes. The pilot schemes may bebased on channel conditions and the relative speed of the user elements16. The length of the short pilot symbols may be dynamically changed aswell as the placement or spacing of the short pilot symbols in the TTI.Further, the number and location of sub-carriers of the short pilotsymbols that are assigned to a given user element 16 or antenna 40thereof may change from TTI to TTI.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present invention. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A method of transmitting sounding pilotinformation, the method comprising: performing, by a mobile terminal:generating the sounding pilot information for a transmitter; and mappingthe sounding pilot information for the transmitter onto at least certainsubcarriers of a first group of subcarriers within a transmission timeinterval (TTI); wherein the transmission time interval (TTI) comprisesone or more pilot symbols and a plurality of traffic symbols; whereinthe one or more pilot symbols comprises at least the first group ofsubcarriers and at least a second group of subcarriers, wherein thefirst group of subcarriers are sounding pilots, wherein the second groupof subcarriers are pilots for demodulation, and wherein the second groupdoes not comprise sounding pilots.
 2. The method of claim 1, whereinsaid generating the sounding pilot information comprises: generating thesounding pilot information with an orthogonal code for the transmitter.3. The method of claim 1, wherein said mapping the sounding pilotinformation comprises: mapping the sounding pilot information for thetransmitter onto at least certain subcarriers of the first group ofsubcarriers, wherein the first group of subcarriers is mapped everyother one of the subcarriers for a block of subcarriers.
 4. The methodof claim 1, further comprising: generating data information for thetransmitter; mapping the data information for the transmitter onto atleast certain of the subcarriers of the plurality of traffic symbols;generating pilot information for the transmitter; and mapping the pilotinformation for the transmitter onto at least certain of the secondgroup of subcarriers of the at least one pilot symbol.
 5. The method ofclaim 1, wherein said mapping the sounding pilot information comprises:mapping the sounding pilot information for the transmitter onto at leastcertain subcarriers of the first group of subcarriers, wherein thesounding pilot information for the transmitter and sounding pilotinformation for one or more other transmitters are multiplexed on thefirst group of sub-carriers.
 6. The method of claim 1, wherein saidgenerating the sounding pilot information comprises generating thesounding pilot information with an orthogonal code for the transmitter;and wherein said mapping the sounding pilot information comprisesmapping the sounding pilot information for the transmitter onto at leastcertain subcarriers of the first group of sub-carriers, wherein thesounding pilot information for the transmitter and sounding pilotinformation for one or more other transmitters, each generated withorthogonal codes, are mapped onto common subcarriers of the first groupof subcarriers.
 7. The method of claim 1, wherein said mapping the soundpilot information comprises: mapping the sounding pilot information forthe transmitter onto at least certain subcarriers of the first group ofsubcarriers, such that the sounding pilot information for thetransmitter and sounding pilot information for one or more othertransmitters are multiplexed in frequency on different subcarriers ofthe first group of subcarriers.
 8. A transmitter, comprising: soundingpilot generation circuitry configured to generate sounding pilotinformation for a transmitter; and subcarrier mapping circuitryconfigured to map sounding pilot information for the transmitter onto atleast certain subcarriers of a first group of subcarriers within atransmission time interval (TTI); wherein the transmission time interval(TTI), comprises one or more pilot symbols; and a plurality of trafficsymbols; wherein the one or more pilot symbols comprises at least thefirst group of subcarriers and at least a second group of subcarriers,wherein the first group of subcarriers are sounding pilots, wherein thesecond group of subcarriers are pilots for demodulation, and wherein thesecond group does not comprise sounding pilots.
 9. The transmitter ofclaim 8, wherein to generate the sounding pilot information, thesounding pilot generation circuitry is further configured to: generatethe sounding pilot information with an orthogonal code for thetransmitter.
 10. The transmitter of claim 8, wherein to map the soundingpilot information, the subcarrier mapping circuitry is furtherconfigured to: map the sounding pilot information for the transmitteronto at least certain subcarriers of the first group of subcarriers,wherein the first group of subcarriers is mapped every other one of thesubcarriers for a block of subcarriers.
 11. The transmitter of claim 8,further comprising: data generation circuitry configured to generatedata information for the transmitter, wherein the subcarrier mappingcircuitry is further configured to map the data information for thetransmitter onto at least certain of the sub-carriers of the pluralityof traffic symbols; and pilot generation circuitry configured togenerate pilot information for the transmitter, wherein the subcarriermapping circuitry is further configured to map the pilot information forthe transmitter onto at least certain of the second group of subcarriersof the at least one pilot symbol.
 12. The transmitter of claim 8,wherein to map the sounding pilot information, the subcarrier mappingcircuitry is further configured to: map the sounding pilot informationfor the transmitter onto at least certain subcarriers of the first groupof subcarriers, wherein the sounding pilot information for thetransmitter and sounding pilot information for one or more othertransmitters are multiplexed on the first group of sub-carriers.
 13. Thetransmitter of claim 8, wherein to generate the sounding pilotinformation, the sounding pilot generation circuitry is furtherconfigured to generate the sounding pilot information with an orthogonalcode for the transmitter; and wherein to map the sounding pilotinformation, the subcarrier mapping circuitry is further configured tomap the sounding pilot information for the transmitter onto at leastcertain subcarriers of the first group of sub-carriers, wherein thesounding pilot information for the transmitter and sounding pilotinformation for one or more other transmitters, each generated withorthogonal codes, are mapped onto common subcarriers of the first groupof subcarriers.
 14. The transmitter of claim 8, wherein to map thesounding pilot information, the subcarrier mapping circuitry is furtherconfigured to: map the sounding pilot information for the transmitteronto at least certain subcarriers of the first group of subcarriers,wherein the sounding pilot information for the transmitter and soundingpilot information for one or more other transmitters are multiplexed infrequency on different subcarriers of the first group of subcarriers.15. A base station, comprising; receive circuitry configured to receiveradio frequency signals through the antennas bearing information fromone or more remote transmitters; wherein the information from a firsttransmitter comprises sounding pilot information; wherein the soundingpilot information is mapped to at least certain subcarriers of a firstgroup of subcarriers within a transmission time interval (TTI); whereinthe transmission time interval (TTI), comprises one or more pilotsymbols and a plurality of traffic symbols; wherein the one or morepilot symbols comprises at least the first group of subcarriers and atleast a second group of subcarriers, wherein the first group ofsubcarriers are sounding pilots, wherein the second group of subcarriersare pilots for demodulation, and wherein the second group does notcomprise sounding pilots.
 16. The base station of claim 15, wherein thereceive circuitry is further configured to receive the sounding pilotinformation encoded with an orthogonal code for the first transmitter.17. The base station of claim 15, wherein the receive circuitry isfurther configured to: receive the sounding pilot information for thefirst transmitter on at least certain subcarriers of the first group ofsubcarriers, wherein the first group of subcarriers is mapped everyother one of the subcarriers for a block of subcarriers.
 18. The basestation of claim 15, wherein the receive circuitry is further configuredto: receive sounding pilot information for the first transmitter on atleast certain subcarriers of the first group of subcarriers, wherein thesounding pilot information for the transmitter and sounding pilotinformation for one or more other transmitters are multiplexed on thefirst group of sub-carriers.
 19. The base station of claim 15, whereinthe receive circuitry is further configured to: receive the soundingpilot information encoded with an orthogonal code for the firsttransmitter on at least certain subcarriers of the first group ofsub-carriers, wherein the sounding pilot information for the transmitterand sounding pilot information for one or more other transmitters, eachgenerated with orthogonal codes, are mapped on common subcarriers of thefirst group of subcarriers.
 20. The transmitter of claim 15, wherein thereceive circuitry is further configured to: receive the sounding pilotinformation for the first transmitter on at least certain subcarriers ofthe first group of subcarriers, wherein the sounding pilot informationfor the transmitter and sounding pilot information for one or more othertransmitters are multiplexed in frequency on different subcarriers ofthe first group of subcarriers.